U.S. patent number 5,271,521 [Application Number 07/980,543] was granted by the patent office on 1993-12-21 for method and apparatus for compensating for changes in viscosity in a two-component dispensing system.
This patent grant is currently assigned to Nordson Corporation. Invention is credited to Jeffrey S. Noss, Richard P. Price, James W. Schmitkons.
United States Patent |
5,271,521 |
Noss , et al. |
December 21, 1993 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for compensating for changes in viscosity in a
two-component dispensing system
Abstract
A two-component mixing and dispensing system for mixing and
dispensing two-component polymeric materials which react chemically
with one another when combined to form a mixture includes a
controller for adjusting the pressure at which at least one of the
components is supplied to a dispenser dependent upon variations in
the parameters which affect the cure time of the mixture.
Inventors: |
Noss; Jeffrey S. (Bay Village,
OH), Price; Richard P. (Parma Heights, OH), Schmitkons;
James W. (Lorain, OH) |
Assignee: |
Nordson Corporation (Westlake,
OH)
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Family
ID: |
25527648 |
Appl.
No.: |
07/980,543 |
Filed: |
November 23, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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943105 |
Sep 10, 1992 |
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640060 |
Jan 11, 1991 |
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640043 |
Jan 11, 1991 |
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Current U.S.
Class: |
222/1; 222/135;
222/63; 222/55; 222/146.2; 222/145.6; 222/145.7 |
Current CPC
Class: |
B01F
15/00025 (20130101); G05D 11/132 (20130101); B29B
7/826 (20130101); B01F 5/0615 (20130101); B29B
7/726 (20130101); B08B 9/08 (20130101); B29B
7/325 (20130101); B29B 7/728 (20130101); B29B
7/7419 (20130101); B29C 48/022 (20190201); B01F
15/0454 (20130101); B29B 7/7433 (20130101); B01F
15/00162 (20130101); B08B 7/02 (20130101); B01F
15/00175 (20130101); B01F 3/08 (20130101); B29C
48/03 (20190201); B29K 2105/0097 (20130101) |
Current International
Class: |
B08B
9/08 (20060101); B08B 7/02 (20060101); B29B
7/00 (20060101); B29B 7/76 (20060101); B29C
47/00 (20060101); G05D 11/00 (20060101); B01F
15/04 (20060101); B01F 15/00 (20060101); G05D
11/13 (20060101); B01F 3/08 (20060101); B67D
005/52 () |
Field of
Search: |
;222/135,145,129,63,55,54,52,146.2,146.5,1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0025871 |
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Apr 1981 |
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EP |
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0223519 |
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May 1987 |
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EP |
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0374300 |
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Jun 1990 |
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EP |
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0473424 |
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Mar 1992 |
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EP |
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91/10551 |
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Jul 1991 |
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WO |
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2163360 |
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Feb 1986 |
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GB |
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Other References
369 Plastics Engineering: pp. 33-35, Machinery, Nov. 1983:
"Exacting RIM process controls help yield higher-quality plastic
parts"..
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Primary Examiner: Bollinger; David H.
Attorney, Agent or Firm: Wood, Herron & Evans
Parent Case Text
This is a continuation-in-part application of copending U.S. patent
application Ser. No. 07/943,105 to Schmitkons et al, filed Sep. 10,
1992 and entitled "Method and Apparatus For Metering Flow of A
Two-Component Dispensing System", which is a continuation of U.S.
patent application Ser. No. 07/640,060 to Schmitkons et al, filed
Jan. 11, 1991, now abandoned; and a continuation in-part
application of copending U.S. patent application No. 07/640,043 to
Schmitkons, et al, filed Jan. 11, 1991 and entitled "Method and
Apparatus For Cleaning A Mixer", the disclosure of each is hereby
incorporated by reference herein, and all of which are owned by the
assignee of this invention.
Claims
What is claimed is:
1. A mixing and dispensing system for mixing and dispensing at
least two different polymeric materials which react chemically with
one another when combined, said system comprising:
a dispenser having a plurality of liquid flow inlets and an
outlet;
first and second pump means for supplying a different liquid
polymeric material under pressure to each of said liquid flow
inlets of said dispenser, the liquid polymeric materials being
combined with one another within said dispenser to form a
mixture;
control means for adjusting the pressure at which at least one of
said liquid polymeric materials is supplied to said inlets of said
dispenser, when the flow of said materials through said dispenser
is terminated, as a function of a change in the viscosity of the
mixture of said liquid materials within said dispenser, said
control means including a bypass flow path around at least one of
said first and second pump means and an adjustable pressure
regulator means for regulating the pressure in said bypass flow
path.
2. The apparatus of claim 1 in which said first pump means includes
a first pumping unit adapted to connect to a source of one liquid
polymeric material and to one of said inlets of said dispenser, and
said second pump means includes a second pumping unit adapted to
connect to a source of a different liquid polymeric material and to
another one of said inlets of said dispenser.
3. The apparatus of claim 2 in which said
adjustable pressure regulator means is connected between at least
one of said first and second pumping units and said dispenser, for
regulating the pressure at which at least one of said liquid
polymeric materials is supplied to said dispenser;
means for adjusting said pressure regulator means to very the
pressure at which said at least one liquid polymeric material is
supplied to said dispenser dependent on changes in the viscosity of
the mixture formed within said dispenser.
4. The apparatus of claim 3 in which said means for adjusting said
pressure regulator means includes at least one of the
following:
(i) means for determining the length of time during which flow of
said liquid polymeric materials through said dispenser is
terminated;
(ii) means for sensing changes in temperature of said mixture
within said dispenser; and
(iii) means for determining the ratio of said liquid polymeric
materials supplied to said dispenser.
5. The apparatus of claim 1 wherein said control means
comprises:
a means for controlling the inlet pressure of each of said
polymeric materials at said dispenser after the flow of materials
through said dispenser is terminated so that said inlet pressures
are a predetermined function of the pressure which was maintained
at said dispenser when said materials were flowing through said
dispenser.
6. The apparatus of claim 1 further comprising:
purge means, operatively connected to said control means, for
purging the mixture of said liquid materials from said dispenser
prior to resumption of flow of said liquid polymeric materials
through said dispenser in the event the viscosity of the mixture
exceeds a predetermined level.
7. The apparatus of claim 6 in which said purge means includes
means for pulsing a flow of one of said liquid polymeric materials
through said dispenser, while terminating the flow of the other
liquid polymeric material, to force at least a partially cured
mixture of such materials out of said dispenser.
8. The apparatus of claim 6 in which the mixture of liquid
polymeric materials forms a cured layer along the internal walls of
said dispenser, said purge means including means for heating said
dispenser to reduce the shear strength with which said cured layer
adheres to said internal walls, and means for introducing a flow of
one of said liquid polymeric materials into said dispenser while
terminating the flow of the other of said polymeric materials.
9. The apparatus of claim 6 in which said first pumping unit is
adapted to connect to a source of one liquid polymeric material and
to one of said inlets of said dispenser, and said second pumping
unit is adapted to connect to a source of a different liquid
polymeric material and to another one of said inlets of said
dispenser.
10. The apparatus of claim 9 in which said
adjustable pressure regulator means is connected between at least
one of said first and second pumping units and said dispenser, for
regulating the pressure at which at least one of said liquid
polymeric materials is supplied to said dispenser;
means for adjusting said pressure regulator means to vary the
pressure at which said at least one liquid polymeric material is
supplied to said dispenser dependent on changes in the viscosity of
the mixture formed within said dispenser.
11. The apparatus of claim 10 in which said means for adjusting
said pressure regulator means includes at least one of the
following:
(i) means for determining the length of time during which flow of
said liquid polymeric materials through said dispenser is
terminated;
(ii) means for sensing changes in temperature of said mixture
within dispenser; and
(iii) means for determining the ratio of said liquid polymeric
materials supplied to said dispenser.
12. The method of mixing and dispensing at least two different
polymeric materials which react chemically with one another when
combined, comprising:
supplying different liquid polymeric materials, under pressure,
from first and second pump means to a dispenser wherein said
materials are combined to form a mixture which is emitted from the
dispenser;
terminating the flow of the mixture from the dispenser;
adjusting the pressure at which at least one of the liquid
polymeric materials is supplied to the dispenser, prior to
resumption of the flow of the mixture from the dispenser, as a
function of a change in viscosity of the mixture within the
dispenser, said adjusting step performed via operation of an
adjustable pressure regulator means adapted to regulate the
pressure in a bypass flow path around at least one of said first
and second pump means.
13. The method of claim 12 in which said step of adjusting the
pressure comprises adjusting the pressure at which at least one of
the liquid polymeric materials is supplied to the dispenser as a
function of the time during which the mixture remains within the
dispenser before flow of the mixture from the dispenser is
resumed.
14. The method of claim 12 in which said step of adjusting the
pressure comprises adjusting the pressure at which at least one of
the liquid polymeric materials is supplied to the dispenser as a
function of the ratio with which the liquid polymeric materials are
supplied to the dispenser.
15. The method of claim 12 in which said step of adjusting the
pressure comprises adjusting the pressure at which at least one of
the liquid polymeric materials is supplied to the dispenser as a
function of the temperature of the mixture within the
dispenser.
16. A method of mixing and dispensing comprising the steps of:
a. intermittently dispensing a mixture of a first and second
pressurized liquid polymeric material from an outlet of a
dispenser, the first and second liquid polymeric materials supplied
to the dispenser by first and second pump means, respectively;
b. determining a steady state inlet pressure for each liquid
polymeric material supplied to the dispenser from said first and
second pump means when said mixture is dispensing under steady
state flow conditions;
c. determining and maintaining an off inlet pressure as a function
of the respective steady state inlet pressures of each liquid
polymeric material when said mixture is not being dispensed from
the dispenser; and
d. adjusting the off inlet pressure prior to resumption of the flow
of the mixture from the dispenser, as a function of a change in
viscosity of the mixture within the dispenser, said adjusting step
performed via operation of an adjustable pressure regulator means
adapted to regulate the pressure in a bypass flow path around at
least one of said first and second pump means.
17. The method of claim 16 wherein the off inlet pressure of each
liquid polymeric material of step (c) is substantially equal to the
respective steady state inlet pressure or is a multiple thereof;
and
wherein said step of adjusting the off inlet pressure comprises
adjusting the pressure at which at least one of the first and
second liquid polymeric materials is supplied to the dispenser as a
function of at least one of the following: (i) the time during
which the mixture remains within the dispenser before flow of the
mixture from the dispenser is resumed; (ii) the ratio with which
the liquid polymeric materials are supplied to the dispenser; and
(iii) the temperature of the mixture within the dispenser.
Description
FIELD OF THE INVENTION
This invention relates to two-component mixing and dispensing
systems and, more particularly, to systems for mixing and
dispensing two different polymeric materials which react chemically
with one another when combined to form a mixture whose viscosity
varies with changes in operating parameters such as temperature,
cure time and the ratio of such materials.
BACKGROUND OF THE INVENTION
Two-component polymeric materials such as reactive adhesives,
paints, gasket materials, and caulking materials comprise two
separate components which react chemically with one another when
intermixed. For example, two-component hot melt polymeric materials
used in adhesive applications include a polymeric material and a
second material such as a hardener. These types of hot melt
adhesives, and other two-component polymeric materials, are
dispensed from a system in which the two components are supplied in
a predetermined ratio from separate metering pumps to a
mixer/dispenser where they are intermixed with one another and
dispensed onto a substrate. In such a system, if too much of one
component is applied, then the characteristics of the combined
mixture of such materials are undesirably altered. It is therefore
important that the ratio of the components of two-component mixing
and dispensing systems be exactly maintained. But this ratio is
particularly difficult to maintain when the materials are supplied
to a mixer/dispenser which is intermittent in operation, i.e.,
which is repeatedly turned on and off. In such applications, loss
of ratio control characteristically occurs for a few seconds
shortly after the dispenser valve is opened during which time a
transient imbalance phenomena occurs caused by the elasticity in
the system and the changing hydraulic pressures associated with
cycling the mixer/dispenser.
Another problem which may occur in intermittent operation of
two-component mixing and dispensing systems is a loss of flow
control of the resulting mixture of the two components. It is
desirous to control the flow rate of the resulting mixture
dispensed to the substrate. However, during the first few seconds
after opening of the mixer/dispenser, the transient imbalance
phenomena described above may result in a loss of control of the
flow rate of the mixture. Additionally, a loss of precise control
of the flow rate of the mixture can occur as a result of changes in
density or viscosity of either of the two components due to
temperature changes thereof. If the mixture is an adhesive, this
may result in less adhesive being applied to the substrate, which,
in turn, may affect the bonding of materials.
The aforementioned problems with two-component mixing and
dispensing systems have been addressed in U.S. patent application
Ser. No. 07/640,060. As disclosed in that application, the exact
ratio of the two components supplied to the mixer/dispenser can be
controlled as a function of the pressure of the two materials at
the inlets to the mixer/dispenser. It was recognized that
maintenance of the desired ratio of such components requires
adjustment and control of the pressure of each component at the
mixer/dispenser during the off cycle of the operation. In order to
achieve such control, the system of application Ser. No. 07/640,060
includes two back pressure controls, each of which is interposed
between the intermittently operable mixer/dispenser and a metering
gear pump connected to a source of one of the components of liquid
material. Each back pressure control comprises a bypass flow path
around each metering pump and an adjustable pressure regulator
contained in that bypass path. Additionally, each bypass flow path
includes a flow control valve which is closed when the dispenser
flow control valve is open and vice versa. To control the pressure
of each component at their respective inlets to the dispenser, the
adjustable pressure regulator in each bypass flow path is operated
either manually or automatically to adjust the pressure at the
inlets to the mixer/dispenser when the flow control valve is closed
so that such pressure is equal to or a function of the steady state
flow pressure at the inlet to the mixer/dispenser when its valve is
open.
Despite the above-mentioned improvements in the control system
associated with two-component mixing and dispensing systems
disclosed in U.S. patent application Ser. No. 07/640,060,
additional problems have been discovered with intermittent
operations of systems of this type. As described above, the two
components are supplied separately from individual sources into the
mixer/dispenser where they are combined with one another to form a
mixture prior to deposition onto a substrate. Within a short period
of time, these intermixed materials begin to cure within the
mixer/dispenser which can appreciably increase the viscosity of the
mixture and/or create problems of plugging or clogging of the
mixer/dispenser with cured material. Depending upon the period of
time during which the mixer/dispenser is shut off, and other
parameters such as temperature of the components and the ratio at
which such components are supplied to the mixer/dispenser, a
pressure substantially in excess of the steady state pressure may
be required to obtain the desired volumetric or mass flow rate of
each component, and therefore the ratio and the total flow rate of
the mixture from the mixer/dispenser when its valve is again opened
and flow is resumed.
SUMMARY OF THE INVENTION
It is therefore among the objectives of this invention to provide a
method and apparatus for mixing and dispensing two different
polymeric materials which react chemically with one another when
combined to form a mixture, which accounts for changes in viscosity
of the mixture resulting from factors which affect the cure rate of
the mixture, and which ensures that the volumetric or mass flow
rate of each component, and therefore the ratio and the total flow
rate of the mixture emitted from the apparatus remains
substantially constant, particularly during intermittent operation
of the system.
These objectives are accomplished in a two-component mixing and
dispensing system of the type disclosed in the above-mentioned U.S.
patent application Ser. No. 07/640,060, the disclosure of which is
incorporated by reference in its entirety herein, with the addition
of structure for adjusting the pressure at which one or both of the
components are supplied to the mixer/dispenser dependent on (1) the
length of time during which operation of the mixer/dispenser has
been terminated, (2) temperature changes of the mixture and, (3)
the ratio at which the two components are supplied to the
mixer/dispenser. In the event the pressure required to resume the
desired flow rate of mixture from the mixer/dispenser exceeds a
predetermined level, the control system of this invention is
effective to initiate a purge cycle to either clean cured mixture
from the mixer/dispenser, or require replacement of the
mixer/dispenser, prior to resumption of the dispensing
operation.
As disclosed in application Ser. No. 07/640,060, the system therein
comprises a pair of metering gear pumps each having an input side
connected to a source of one of the two components and an output
side connected to an inlet of a mixer/dispenser. During steady
state conditions, the two metering gear pumps supply a
predetermined ratio of the two components into the mixer/dispenser
at steady state pressure and steady state flow wherein the
components are intermixed to form a mixture for deposition onto a
substrate. In order to maintain a constant mass flow rate or
volumetric flow rate of each component to the mixer/dispenser,
particularly when the mixer/dispenser is operated intermittently, a
back pressure control is associated with each metering gear pump
which is effective to maintain a predetermined pressure of each
component at its respective inlet to the mixer/dispenser.
This invention is predicated upon the concept of providing a
further control capability in a system of the type described above.
This control capability is based on the premise that higher
viscosity materials require more force to move than lower viscosity
materials. As the mixture of the two components within the
mixer/dispenser changes in viscosity, e.g., due to increasing cure
time while the dispenser remains off or increases in temperature or
changes in the ratio of the two components, a change in force is
required to eject the mixture from the mixer/dispenser at the same
volumetric or mass flow rate obtained during steady state
operation.
The control system herein is provided with inputs corresponding to
each of the three system parameters which affect curing, and,
hence, viscosity, of the mixture, i.e., mixer/dispenser off time,
mixture temperature and the ratio of the two components. The
control system includes a computer which employs an experimentally
generated look-up table, or a mathematical formula, to determine
the appropriate adjustment in pressure of either one of the two
components supplied to the inlets of the mixer/dispenser dependent
on the sensed parameters. In turn, the controller operates the
pressure regulator associated with each back pressure control to
vary the pressure at which one or both of the two components are
supplied to the mixer/dispenser, so that when the valve of the
mixer/dispenser is opened an appropriate force is applied to the
mixture within the mixer/dispenser to eject it therefrom at the
desired flow rate and ratio.
In the event the change in pressure required to obtain the desired
flow rate exceeds operating parameters of the system, the control
system is operative to initiate a purge cycle of the type disclosed
in U.S. patent application Ser. No. 07/640,043, filed Jan. 11, 1991
to Schmitkons et al, entitled "Method and Apparatus For Cleaning A
Mixer", which is owned by the assignee of this invention and the
disclosure of which is incorporated by reference in its entirety
herein. Alternatively, the control system can provide the operator
with an alarm signalling he or she to replace the clogged
mixer/dispenser with a new one.
DESCRIPTION OF THE DRAWINGS
The structure, operation and advantages of the presently preferred
embodiment of this invention will become further apparent upon
consideration of the following description, taken in conjunction
with the accompanying drawings, wherein:
FIG. 1 is a diagrammatic illustration of a two-component mixing and
dispensing system embodying the invention of this application;
FIG. 2 is a cross sectional view of the static mixer in the system
of FIG. 1;
FIG. 3 is a cross sectional view taken generally along line 3--3 of
FIG. 2 illustrating the static mixer in a condition where it is
completely cleared of cured material;
FIG. 4 is a view similar to FIG. 3 except after a period of
operation of the mixer where a layer of cured material has
collected on the mixer walls;
FIG. 5 is a view similar to FIGS. 3 and 4 except after the
application to heat to the static mixer, and after the introduction
of flushing material therein to dislodge the cured material;
FIG. 6 is a view similar to FIG. 5 wherein the cured material is
transmitted out of the static mixer by the purging material;
and
FIG. 7 is a schematic depiction in the form of a flow chart of the
operation of the control system of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The overall construction and operation of the two-component system
10 illustrated in FIG. 1 is provided initially, which, except as
specifically set forth below, forms no part of this invention and
is fully disclosed in U.S. patent application Ser. No. 07/640,060
mentioned above. The control system of this invention is described
separately below in connection with a discussion of pressure
control within system 10.
Overall System Construction
With reference to FIG. 1, there is illustrated one embodiment of a
two-component system 10 for mixing and dispensing two different
materials, such as two different hot melt polymeric materials. Hot
melt materials are those materials which are solid at room or
ambient temperature but which, upon application of heat, can be
converted to the liquid state. When dispensed at ambient
temperature, molten hot melt materials quickly return to the solid
state. The two-component hot melt system described herein is
particularly suited to the application of a two-component hot melt
adhesive such as the Curemelt 560 Series two component hot melt
manufactured by The Union Camp Co. This system could as well,
though, be utilized for mixing and dispensing cold materials and
materials other than adhesives, as for example, paints or gasket or
caulking materials. Additionally, the system may be used to
dispense hot melt solid or foam materials.
The two-component mixing and dispensing system 10 comprises two hot
melt applicators 12 and 14, two metering pumps 16 and 18, and a
mixer/dispenser 20. Additionally, there is associated with each
metering pump 16 and 18 a back pressure control means 22, 24,
respectively.
In this embodiment of the invention, the hot melt applicators 12
and 14 are two different types of applicators because of the
different volumes of material which each is required to melt and
pump to the metering pumps 16 and 18 via the interconnecting
conduits 26 and 28, respectively. The hot melt applicator 12 is
operative to melt and supply under pressure from a pump contained
internally of the applicator a first polymeric material which is
utilized in less volume than the component supplied from the bulk
hot melt applicator 14. One hot melt applicator 12 suitable for
melting and pumping to the system the smaller volume polymeric
component of this application is completely disclosed in U.S. Pat.
No. 3,964,645 issued Jun. 22, 1976 and assigned to the assignee of
this application. Similarly, a bulk melter 14 suitable for melting
and supplying under pressure the main or high volume polymeric
component utilized in this application is completely disclosed in
U.S. Pat. No. 4,073,409 issued Feb. 14, 1978.
The metering pumps 16 and 18 may be gear-type, motor-driven pumps
operative to supply molten polymeric material via the conduits 26
and 28, respectively, to the dispenser 20. The volume at which each
component is supplied to the dispenser 20 is controlled by the
speed of the variable speed motors 16a, 18a utilized to drive the
gear 16b, 18b of the pumps 16 and 18, respectively. The metering
pumps 16, 18 are coupled or linked electrically such that the ratio
of the volume or mass dispensed from one metering pump is in
proportion to the volume or mass dispensed from the other one. From
the gear pump 16, the molten polymeric material derived from the
hot melt applicator 12 is supplied to the dispenser 20 via a
conduit 30 through an air-operated solenoid valve 32 of the
dispenser 20. Similarly, from the metering pump 18, the main or
high volume polymeric material is supplied via a conduit 34 to
another air-operated solenoid valve 36 of the dispenser 20. As
described below, the operation of solenoid valves 32 and 36 is
controlled by an electrical control 75 which is connected thereto
by lines 33 and 37, respectively.
As shown in FIG. 2, these valves 32 and 36, in turn, are
individually operable to control the flow of two different
components into the dispenser 20 where the two different materials
are for the first time combined. From the dispenser, the two
materials flow through a static mixer 40 having an outer wall 41
and an internal mixing element 43 of the type which is operative to
repeatedly divide and recombine the mixture in the course of
passage through the mixer 40 such that by the time the two
components reach the discharge orifice 42 of the dispenser 20, the
two components have been thoroughly mixed. A static mixer is
illustrated in the Figs. for purposes of describing the purging
operation of this invention, but it should be understood that the
method and apparatus herein is equally applicable to other types of
mixers including dynamic mixers.
In one presently preferred embodiment shown in FIG. 2, an electric
resistance cable heater 45 is helically wound around the outer wall
41 of mixer 40 where it is permanently brazed into position using a
high melting point brazing alloy (not shown). This cable heater 45
preferably includes an internal-type thermocouple connected by a
thermocouple lead to a closed-loop feedback control which forms
part of the "electrical control" indicated schematically at 75 in
FIG. 1. Power leads and a ground line are also connected between
the cable heater 45 and the electrical control 75. The thermocouple
sends signals to the electrical control 75, as depicted in FIG. 2,
which are correlated to the temperature of mixer 40 and are used to
control the operation of cable heater 45.
A chemical reaction occurs between the two polymeric materials in
the course of passage through the mixer 20, and continues after the
components are dispensed from the outlet 42 thereof. In many
applications, one component of the two-component system is a
hardener which, when combined with the other component, causes that
component to acquire its desired properties.
Each back pressure control means 22, 24 includes a bypass flow path
46, 48 around the gear pump 16, 18 with which it is associated.
This bypass flow path comprises a flow conduit extending from the
discharge side of the gear pump and its conduit 30, 34 to the input
side of the gear pump and its input conduit 26, 28. Included in
this flow path is a pneumatically operated flow control valve 52,
52', connected to the electrical control by lines 53 and 55, and an
adjustable pressure regulator means 54, 54' connected in series in
the bypass flow path. The adjustable pressure regulator means may
take the form of a simple adjustable needle valve forming an
adjustable restrictor in the bypass flow path 46, 48 or it may take
the form of an adjustable pressure regulator valve. As explained
more fully hereinafter, the function of this adjustable pressure
regulator means 54, 54' is to regulate and control the back
pressure in the bypass flow path 46, 48 when the flow control
valves 52, 52' are open.
Additionally, each bypass flow path 46, 48 includes an overload
pressure regulator in the form of a pressure relief valve 56, 56'
connected in parallel with the flow control valve 52, 52' and
adjustable pressure control means 54, 54'. The function of the
overload pressure relief valve 56, 56' is to bypass liquid from the
discharge side of the metering pump to the inlet side in the event
that the pressure on the discharge side of the metering pump
exceeds a preset pressure substantially above the operating
pressure at which the particular component is to be supplied from
the applicator 12 or 14 to the dispenser 20.
Air pressure is supplied alternatively to the air-pressure operated
solenoids 32, 36 of the dispenser 20 and the pneumatically operated
flow control valves 52, 52' of the back pressure control means 22
and 24 as determined by electrical control 75. That is, when air
pressure is supplied to the solenoids 32, 34 of the dispenser via
lines 33 and 37 so as to cause those valves to open and permit flow
of liquid to the dispenser, air pressure is supplied via lines 53
and 55 to the flow control valves 52, 52' to close the bypass flow
paths. On the other hand, when the solenoids 32, 36 are closed, and
flow of valves 52, 52' are opened.
In the operation of the system 10 illustrated in FIG. 1, the first
or smaller volume component polymeric material is supplied in solid
form to the hot melt applicator 12. In this example, this component
is referred to as the smaller volume component, or component "A",
but it could obviously be supplied at the same volume as the second
component and still be within the practice of this invention. In
the applicator 12, this material is melted and converted from the
solid to the liquid state. This liquid smaller volume component A
is supplied via a pump contained in the applicator 12 under
pressure to the metering pump 16. The metering pump is operative to
supply the molten liquid component A at a desired flow rate to the
discharge side of the metering pump. Assuming that the flow control
valve 32 of the dispenser 20 is closed, the output flow from the
metering pump 16 is routed via the now open flow control valve 52
and pressure regulator means 54 in the bypass flow path 46, back to
the input side of the gear pump 16. This bypass flow of component A
will continue until the dispenser flow control valve 32 is opened.
Similarly, the high volume or main component, component "B" solid
material is melted by the bulk hot melt applicator 14 and is
supplied under pressure from a pump contained internally of the
bulk melter 14 to the metering pump 18. So long as the flow control
valve 36 of the dispenser remains closed, material B continues to
flow through the metering pump 18 and then through the bypass flow
path 48, through the open flow control valve 52' and the pressure
regulator means 54', back to the input side of the metering pump
18. When the flow control valves 32, 36 of the dispenser are
opened, the flow control valves 52, 52' in the bypass flow paths
around the metering pumps are simultaneously closed. Thereby, each
component is permitted to flow from the metering pump via the
conduits 30, 34 into the dispenser 20 and through the mixer 40 to
the discharge orifice 42 of the dispenser.
Initial Pressure Control At Inlets To Mixer/Dispenser
In accordance with the practice of one embodiment of this
invention, the pressure of the two components A and B at the input
side of the dispenser 20 is in the steady state flow condition when
the two components are being mixed and dispensed through the
dispenser 20. When the flow control valves 32, 36 of the dispenser
20 are closed and the flow control valves 52, 52' are open, the
pressure regulator means 54, 54' are adjusted so as to maintain the
pressure at the inlets to the dispenser 20 at about the same
pressure as was recorded by pressure transducer and/or pressure
read-out gauges 60, 62 on the input sides of the dispenser 20 in
the steady state flow condition, i.e., when the flow control valves
32, 36 of the dispenser were open and the flow control valves 52,
52' were closed.
In practice it is preferred that the pressure regulator means 54,
54' are automatically adjusted. When operated automatically, the
adjustable pressure regulator means 54, 54' may be adjusted by
utilizing a closed loop control circuit, including a computer or
programmable controller as part of the electrical control 75, to
manipulate the adjustment of the pressure regulator means 54, 54'
so as to maintain the input pressure to the dispenser as a function
of the pressure that prevailed during steady state flow immediately
prior to the closing of the flow control valves 32, 34. Preferably,
in such an automatic control, the steady state pressure is
determined for each cycle and the valves 54, 54' adjusted
accordingly. This can be accomplished by utilizing pressure
transducers for the gauges 60, 62 to provide input signals via
lines 61 and 63, respectively, to the electrical control 75. The
pressure settings of the pressure regulator means 54, 54' may then
be adjusted by the electrical control 75 acting on the pressure
control means 54, 54' by signals transmitted via leads 72, 74.
Thus, the pressure reading at the pressure gauge or transducer 60
located at the inlet to the dispenser will be substantially equal
to or a function of the steady state flow pressure when there is no
material flowing through the dispenser.
Flow Rate Adjustment To Compensate For Temperature Variations
As mentioned hereinabove, it is important to maintain the mass
ratio of two components of a two-component mixing and dispensing
system in order to have the resulting mixed components have the
desired properties. In the case of paint, this may be a color or a
drying time, or in the case of an adhesive, this may be a desired
adhesive property and cure time. Since mass is a function of volume
and density, and since density is a function of temperature, the
volume of materials supplied to the dispenser by the metering pumps
16 and 18 must be varied in accordance with the temperature of the
components if a fixed mass ratio between the two-component
materials is to be maintained.
For example, if the temperature of the material supplied by
metering pump 16 changes in temperature by 30.degree. C., and if
this material has specific gravity to temperature properties that
will result in a specific gravity change of 2.5%, then the control
75 will cause the variable speed motor 16a to vary the speed of the
metering pump by that same 2.5% in order to maintain the same fixed
total mass flow rate of materials dispensed from the dispenser
20.
To maintain the fixed mass flow rate through the pumps 16, 18,
temperature measuring devices 64, 66, such as, for example, a
thermocouple or an RTD, are provided for utilization in a closed
loop control circuit. It is preferred that a temperature measuring
device 64, 66 is located within each metering pump to provide an
electrical signal indicative of the temperature of the liquid
component material contained within the pump. The signals are
furnished via leads 69, 71 to the electrical control 75 which may
contain a computer or programmable controller. The electrical
control 75 also includes drive controls 68 and 70, such as SCR
drives, for controlling the speed of the motors 16a and 16b, via
lines 77 and 79. In response to the temperature signals from lines
69, 71, the electrical control 75 provides signals to the
respective drive control 68, 70 which, in turn, adjust the speed of
motors 16a, 16b, accordingly.
Mixing of Components And Purging Cured Mixture From Dispenser
With reference to FIGS. 2 and 3, component A from the hot melt
applicator 12 and component B from the hot melt applicator 14 flow
through valves 32, 36, respectively, into the dispenser 20. As
mentioned above, the internal mixing element 43 is operative to
repeatedly divide and recombine the components A and B so that they
are thoroughly mixed when they reach the discharge orifice 42. As
shown in FIG. 3, when the static mixer 40 first begins operation,
the intermixed components A and B flow through essentially clear,
unobstructed flow paths 72 and 74 defined by the spiral-shaped,
internal mixing element 43 of the static mixer 40. Over a period of
time, and particularly where the system 10 is operated
intermittently, components A and B chemically react with one
another within the interior 49 of static mixer 40 and at least
partially cure therein to form a mixture of increased viscosity. A
method for periodically flushing or purging the partially cured
mixture of components A and B from the mixer interior 49 to delay
the onset of the formation of a layer of cured material 76 of the
type shown in FIG. 4 is disclosed in U.S. patent application Ser.
No. 07/640,043, which is briefly discussed below.
Preferably, the flushing or purging of the partially cured mixture
of components A and B is accomplished as follows. The low volume
flow from hot melt applicator 1 is first discontinued by either
shutting off the gear pump 16 or bypassing flow from the conduit 30
by operation of the flow control valve 52 in the manner described
above. Having cut off the flow of component A through conduit 30,
the high volume flow of component B through conduit 34 is utilized
to purge or flush the mixer interior 49. Flow of this component B
into the static mixer 40 is accomplished as described above, except
that such flow is preferably pulsed or intermittently interrupted
such as by turning on and off the metering gear pump 18, or by
alternately directing the flow of component B into the bypass flow
path 48 instead of through conduit 34 as described above. In either
case, the flow of component B through conduit 34 into the interior
49 of static mixer 40 is preferably allowed to proceed for a
predetermined interval, such as about two seconds, and then is
discontinued for a predetermined time interval such as about two
seconds, so that a pulsed flow of component B is introduced into
the mixer interior 49.
It has been found that the pulsed or intermittently interrupted
flow of component B or other purging material into the mixer
interior 49 effectively flushes away at least a portion of the
mixture of components A and B residing within the mixer 40 which
has partially cured. It is believed that the pulsed flow of
component B into the mixer 40 has the effect of increasing the
"effective viscosity" of such material, which, in turn, increases
the shear force which the component B flushing material applies to
the partially cured mixture within the mixer interior 49. After
being injected into the static mixer 40 for a period of about two
seconds, it is believed that the flushing material stops or at
least slows down during the following two second period when the
flow is discontinued. This slowing or stoppage of the movement of
component B within the mixer interior 49 increases its effective
viscosity. When a new pulse or flow of component B is then
introduced into the mixer interior 49, the component B flushing
material previously introduced into the mixer 40 is pushed
forwardly, and, because of its high effective viscosity, imposes a
comparatively high shear force on at least a portion of the
partially cured mixture of components A and B in the mixer interior
49. The pulses of the component B flushing material are continued
for a sufficient period of time to force at least a portion of the
partially cured mixture of components A and B from the mixer
interior 49 through the discharge outlet 42. For example, the
above-described purging operation has been successfully conducted
over a time period on the order of about 30 seconds, or until about
one-tenth to one-eighth of a pound of component B has been flushed
through the mixer 40. When the operation of system 10 is resumed,
the mixer 40 is effectively cleared of at least some of the
partially cured mixture of components A and B which had been
building up therein.
It is recognized that even with the purging operation described
above, wherein a pulsed flow of component B or other purging
material is introduced into mixer 40, the inner surface of the
mixer wall 41 and the surfaces of the internal mixing element 43
nevertheless eventually become covered with a layer of deposited
material which is believed to be cured material 76, or possibly a
combination of cured and uncured material. As viewed in FIG. 4,
this phenomenon is analogous to arteriosclerosis in human arteries
where a layer builds on the inner walls and restricts the flow of
blood. In the system 10 herein, the mixture of components A and B
cannot be prevented from curing within the static mixer 40 and it
gradually begins to form the layer of deposited or cured material
76 on the internal walls of the mixer 40. As used herein, the term
"walls" is meant to refer to both the inner surface of outer wall
41 and the surfaces of internal mixing element 43.
Once some of the deposited or cured material forms on the mixer
walls, the mixture of components A and B which is subsequently
introduced into the mixer 40 tends to continue to build up along
the walls. This is because the velocity profile of the mixture
within the flow passages 72, 74 is such that the material at the
center of the passages 72, 74 has the highest velocity, while that
portion along the walls has a velocity approaching zero which
allows it to be deposited with the material already present on the
mixer walls. As a result, the layer of cured material 76 gradually
continues to increase in thickness until the flow passages 72 and
74 through the mixer interior 49 become so clogged and restricted
that little flow can be obtained through the mixer 40 and/or the
components A and B are ineffectively mixed together. This condition
can be determined by sensing the pressure across the static mixer
40 with a pressure sensor 77 of any commercially available
type.
When the condition of the interior 49 of the static mixer 40 is at
a point such as illustrated in FIG. 4, and the pressure drop across
the mixer 40 reaches a predetermined upper limit, the second aspect
of the method of this invention is employed to remove the layer of
cured material 76 from the mixer walls. Initially, the flow of both
components A and B to the mixer 40 is discontinued either by
shutting off metering pumps 16, 18 or recirculating their flow
through bypass flow paths 46, 48, in the manner discussed above.
The cable heater 45 or heating coil 49 is then energized to apply
heat to the outer wall 41 of mixer 40. Preferably, the cable heater
45 or heating coil 49 is operated by the electrical control 75 at a
temperature of components A and B, but less than their
decomposition temperature. Because the outer wall 41 and internal
mixer element 43 of the mixer 40 are preferably formed of stainless
steel, or other suitable thermally conductive metallic material,
the heat from cable heater 45 of heating coil 49 is quickly and
efficiently transferred to all of the walls of the mixer 40.
The walls of mixer 40 therefore become heated much more quickly
than the cured material 76 as a whole which is adhered thereto.
This is because such walls are much more thermally conductive then
the polymeric components A and B forming the layer of cured
material 76. As a result, those portions of the layer of cured
material 76 which contact the inner surface of outer wall 41 of the
internal mixing element 43 of mixer 40 are quickly elevated to a
relatively high temperature, whereas the inner portions of the
layer of cured material 76 remain at a lower temperature. Having
elevated the temperature of the portions of cured material 76 which
contact the mixer walls, the shear strength of such material
thereat decreases and this reduces the bond or force with which the
layer of cured material 76 attaches to the mixer walls.
Once the desired temperature within the mixer is obtained for a
period sufficient to reduce the shear strength or force of
adherence of the layer of cured material 76 to the mixer walls, a
flow of flushing or purging material is introduced into the mixer
interior 49. Preferably, the flow of component B into the mixer 40
is resumed at high hydraulic pressure and at a normal application
temperature to accomplish the flushing operation. The hydraulic
pressure at which the component B enters the mixer 40 varies in
accordance with the extent of the restriction of the flow passages
72 and 74 caused by the layer of cured material 76. The component B
is introduced at a constant flow rate, e.g., about 10 pounds per
hour, and when it initially enters mixer 40, the hydraulic pressure
is relatively high, e.g., on the order of about 1800 psi. This
pressure then decreases to levels on the order of about 200 psi as
cured material exits the mixer 40, with component B being supplied
at constant flow rate.
As viewed in FIGS. 5 and 6, the flow of flushing material such as
component B is effective to first dislodge the layer of cured
material 76 from the outer wall 41 and internal mixing element 43
of mixer 40. The layer of cured material 76 fails or breaks away at
the mixer walls, instead of at another location along the thickness
of such layer of cured material 76, because of the aforementioned
reduction of shear strength of the layer of cured material 76 at
the mixer walls. Additionally, the relatively low temperature
component B has a high effective viscosity when introduced into the
mixer 40 which maximizes the shear force which component B applies
to the layer of cured material 76.
After the layer of cured material 76 is broken away from the mixer
walls, the component B flushing material transmits the cured
material 76 as a slug through the mixer 40 and out its discharge
outlet 42. See FIG. 6. Upon completion of this flushing or purging
operation, the temperature of the mixer 40 is allowed to return to
a normal level and resumption of operation of the system 10 can
then proceed.
System Adjustment to Account For Changes In Viscosity of
Mixture
As mentioned above, a principal aspect of this invention is
predicated upon the concept of adjusting the pressure at which
components A and B are delivered to the dispenser 20 through lines
30 and 34, respectively, dependent on changes in viscosity of the
mixture of components A and B as it cures within the dispenser 20.
The cure rate of the mixture of components A and B within the
dispenser 20 is dependent on three parameters, namely (1) the ratio
of component A to component B; (2) the temperature to which the
mixture is exposed within the dispenser 20; and, (3) the residence
time of the mixture within the dispenser 20. In the presently
preferred embodiment, the system 10 of this invention monitors each
of the three parameters mentioned above, and the electrical control
75 is effective to adjust the "off" pressure within the system 10
dependent on such parameters. This "off" pressure is meant to refer
to the pressure within lines 30 and 34 which carry components A and
B, respectively. Variation of the pressure within lines 30 and 34,
as described above, is obtained by the pressure control means 22
and 24, and, in particular, the adjustable pressure regulators 54
and 54'.
With reference to FIG. 8, a diagrammatic sequence of the pressure
adjustment within system 10 is illustrated. As noted above, this
pressure adjustment is intended to compensate for curing of the
mixture within the dispenser 20 during periods when the mixture is
not being dispensed. Such pressure adjustment is necessary because
as the mixture cures within the dispenser 20, it increases in
viscosity and therefore a greater force is required to discharge it
from the dispenser 20 when dispensing is resumed. Such greater
force is provided by increasing the pressure at which components A
and B flow through lines 30, 34 so that the mixture is ejected from
the dispenser 20 at the desired flow rate upon resumption of the
dispensing operation.
The uppermost box in FIG. 8, labeled with reference number 80, is
entitled "Adjust Off Pressure To Maintain Desired Flow Ratio At
Dispenser Restart". This box 80 refers to the control sequence
exhibited by the system 10 as described in detail above. Adjustment
of the "off" pressure during this operation condition is
accomplished by the pressure control means 22 and 24 and electrical
control 75 as described above, i.e., the pressure regulators 54 and
54' are operated by the electrical control 75 to ensure that the
pressure of components A and B at the dispenser 20 is equal to, or
a function of, the steady state flow pressure. If a dispenser "on"
signal is received during the off pressure adjustment sequence
depicted in box 80, that signal is transmitted from box 82 through
line 84 to initiate "constant flow mode" operation of the system 10
as depicted schematically by box 86 in FIG. 8. The term "constant
flow mode" refers to normal operation of the dispenser 20 in
production wherein either the dispenser 20 is open constantly, or
turned on and off intermittently at short intervals so that curing
of the mixture within dispenser 20 is insignificant.
If a dispenser on signal depicted in box 82 is not received, as
schematically depicted by line 88, the electrical control 75
adjusts the off pressure within lines 30 and 34 carrying components
A and B in order to compensate for curing of the mixture within
dispenser 20. See box 90. In order to execute this adjustment
sequence, the electrical control 75 monitors the three different
parameters within the system 10 which affect curing of the mixture
within dispenser 20, i.e., the ratio of components A and B supplied
to dispenser 20, the temperature of the mixture within dispenser 20
and the residence time of the mixture within the dispenser 20.
The ratio of component A to component B is a function of the speed
of the variable speed motors 16a and 18a utilized to drive the
gears 16b, 18b of the gear pumps 16 and 18, respectively. As the
speed of motors 16a, 18a increases, for example, the volume of
components A and B introduced into lines 30 and 34 increases. The
electrical control 75 sends a signal via lines 92 and 94 connected
to variable speed motor 16a, 18a, respectively, for controlling the
relative volume or ratio of components A and B being introduced to
the mixer/dispenser 20.
As depicted in FIG. 1, the temperature of the mixture within
dispenser 20 is monitored by a temperature sensor 96 connected by a
line 98 to the electrical control 75. The temperature sensor 96 is
effective to send a signal to electrical control 75 representative
of the mixture temperature.
The last parameter which influences curing time of the mixture
within dispenser 20 is residence time. In the presently preferred
embodiment, residence time is measured by a timer (not shown)
contained internally of the electrical control 75. This timer is
activated when the dispenser 20 is first turned off, and measures
the total time during which the mixture is present within dispenser
20 before the dispensing operation is resumed.
The electrical control 75 is effective to process the signals
received from variable speed pump 16a, 18a, from the temperature
sensor 96 and from its internal timer, and employ either a
mathematical formula or an empirically or experimentally determined
look-up table to determine the appropriate adjustment of the
pressure within lines 30 and 34 carrying components A and B.
Depending upon the sensed parameters, the electrical control 75
automatically adjusts pressure regulator 54 and/or 54' so that the
pressure at which the components A and B are supplied through line
30 and 34 to the dispenser 20 increases sufficiently to force the
mixture within dispenser 20 outwardly therefrom at the desired flow
rate when the dispensing operation is resumed. For example, if the
dispenser 20 is shut off for a period of three minutes, the mixture
within dispenser 20 will undergo a mathematically calculable or
empirically determinable amount of curing which, in turn, increases
the viscosity of the mixture. If the dispenser 20 is then opened
after this three minute period, the electrical control 75 has
effectively adjusted the pressure regulators 54 and/or 54' to
increase the pressure with which components A and B are directed
through lines 30 and 34. This increased pressure within lines 30
and 34 exerts a greater force on the now higher viscosity mixture
within dispenser 20, than during steady state operation, so that
the mixture is forced out of the dispenser at a predetermined,
desired flow rate substantially equivalent to the flow rate
obtained before the dispensing operation was interrupted. This same
type of adjustment is made by electrical control 75 in the event
either of the other two parameters which affect curing of the
mixture were also to change, i.e., the relative ratio of components
A and B, or the temperature of dispenser 20.
As schematically depicted in FIG. 8, the above-mentioned adjustment
of the "off" pressure within lines 30 and 34 produces a calculated
or empirically determined pressure within lines 30 and 34 which
must be exerted to obtain the desired flow rate. This adjustment
pressure level is then compared with a predetermined, maximum
pressure necessary for safe operation of the system 10 as depicted
schematically in box 100. If the adjusted, "off" pressure is too
high, as depicted by the line 102 entitled "Yes", the system 10
undergoes a purge operation depicted schematically by the box 104.
In other words, if the pressure necessary to obtain the desired
flow rate of the mixture within dispenser 20 is too high, the
system 10 must undergo a purge operation prior to resumption of the
dispensing operation. This purging operation can be accomplished in
the manner described above and depicted in FIGS. 2-7, or,
alternatively, the dispenser 20 can be physically removed from the
system 10 and replaced by a new mixer/dispenser 20 before
resumption of operation.
On the other hand, if the "off" pressure as adjusted by the
electrical control 75 does not exceed the predetermined maximum
level, schematically depicted by the line 106 labeled "no" in FIG.
8, the electrical control 75 waits for a dispenser "on" signal as
schematically depicted in box 108. If no "on" signal is received,
the operating sequence returns to block 82 as depicted by line 107
in FIG. 8. If the "on" signal is received, indicating resumption of
the dispensing operation, the system enters the constant flow mode
86 described above. This constant flow mode continues until a
dispenser off signal is received, which is depicted schematically
by the box 110. The electrical control 75 then resets to the
beginning of the sequence described above, as indicated by line 112
in FIG. 8, and operation proceeds as described above. If the
dispenser remains on, as depicted by line 114, the constant flow
mode of operation continues.
Accordingly, the diagrammatic flow chart shown in FIG. 8
illustrates the operation of electrical control 75 in controlling
the system pressure to account for curing of the mixture within
dispenser 20 during periods when the dispenser is shut off or in
the event of a change in the other operating parameters of
interest, i.e., temperature and component ratio. It should be
understood that the effect of each of the three parameters
discussed above on the rate of curing of the mixture will vary for
different types of materials and different operating requirements.
It is contemplated that an appropriate mathematical formula can be
derived for each different type or class of two-component materials
to account for the affect of each of the three parameters of
interest. Alternatively, the effect of such parameters can be
determined empirically and/or experimentally to generate a
"look-up" table contained within the software of the electrical
control 75 which is utilized to properly adjust the pressure within
lines 30 and 32, as required.
While the invention has been described with reference to a
preferred embodiment, it should be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *